The present invention relates to coextruded weatherable films for providing weatherable surface coating for numerous substrates. More particularly, the present invention relates to at least a two-layer coextruded flexible film structure including at least one outer weatherable layer and at least one underlying thermoplastic layer.
Various films and film structures that exhibit weather resistant properties are known in the art. For example, various structures employing AES (acrylonitrile-ethylene/propylene rubber-styrene) graft copolymers or ASA (acrylonitrile-styrene-acrylate rubber) graft copolymers are described in U.S. Pat. Nos. 4,438,171; 4,440,825; 4,444,840; and 4,444,841.
U.S. Pat. No. 4,438,171 discloses a coextruded sheet product having a total thickness of from 25 to 500 mils by coextruding an AES weatherable film surface layer on an underlaying thermoplastic sheet. U.S. Pat. No. 4,438,171, however, does not disclose coextruded film structures, but instead discloses coextruded sheet structures.
U.S. Pat. No. 4,438,171 describes a coextruded sheet structure of 25 to 500 mils, the surface layer of the sheet structure being 3 to 150 mils of AES graft polymer. The total thickness of the sheet precludes the sheet from being used in applications where thin films (generally less than 25 mils and preferably less than 10 mils) are used. Thin film generally is made on different types of equipment than thick sheet. There is a difficulty in extruding a thin film on a thick layer due to viscosity differences. A uniform film gauge across a thick sheet structure is not readily achieved. Since different polymer viscosities exist, different flow properties exist. Therefore, at a thicker gauge, it becomes more difficult to coextrude, for example, a 3 mil onto a 25 mil substrate.
U.S. Pat. No. 4,440,825 discloses a thick, foamed two-layer structure more specifically an AES polymer (non-specified EPDM) laminated onto a rigid foamed thermoplastic, such as a foamed ABS or foamed PVC, which is compatible with the AES. The Example in U.S. Pat. No. 4,440,825 describes an unexpanded ABS core 0.10 inches (100 mils) thick (which can be expanded to 400 mils when foamed), with 0.05 inch (50 mils) adjacent solid ABS layers, and AES weatherable skins of 0.025 inches (25 mils) thickness. Accordingly, U.S. Pat. No. 4,440,825 is directed toward very thick sheet production, and not thin films. Also, the structure described in U.S. Pat. No. 4,440,825 is assembled by lamination and not coextrusion.
U.S. Pat. No. 4,444,840 discloses a laminate with a surface monolayer (not a multilayer) produced from calendared 4 to 50 mil AES with the rubber content being 25 to 40 percent. Using the process of U.S. Pat. No. 4,440,840, one can not bind, for example, AES to polyethylene or polypropylene or other nonadhesiveable, non-compatible layers. It is desired to provide a film that can be integrally attached to layers of different polymers, to an adhesive, and not to bind different non-compatible, substrates using an adhesive backed film.
U.S. Pat. No. 4,444,841 discloses an extruded monolayer AES weatherable film having a thickness of from 1 mil to 10 mils and the use of said film as a surface layer on laminates. The laminate disclosed can be a variety of materials including thermoplastics and non-plastic materials. U.S. Pat. No. 4,444,841 describes an AES film of 1 to 10 mils made by a blown film process for lamination to metal or cellulosics. Such a blown film is typically less costly and has a higher quality than a calendered film. It is desired to provide a cast extrusion or calendered film rather than a blown film.
U.S. Pat. No. 4,444,841 does not teach coextrusion or making a multilayered adhesive containing structure. U.S. Pat. No. 4,444,841 teaches that where the AES is "not inherently mutually adhesive" to wood or metal, a suitable material may be applied to the AES film or substrate prior to lamination, which may involve pressure and temperature to assist in adhesion. The Example in U.S. Pat. No. 4,444,841 describes a liquid based heat sensitive polyurethane adhesive being applied to metal to bond the AES film to the metal, but does not teach a coextruded adhesive layer on the AES. There is still a need in the industry for a multilayer film with improved properties over a monolayer film such as taught in U.S. Pat. No. 4,444,841.
Typically, monolayer AES-type films require an aqueous or solvent-based liquid adhesive that adheres both to a substrate and the film for application of the film to the substrate. For example, a liquid adhesive is required to bond a wood substrate to a film. Also needed is the requisite equipment to apply and dry the liquid adhesive prior to applying the film to the substrate. Such a process is costly and complex due to stringent industrial hygiene requirement and environmental concerns and solvent recovery or disposal requirements. It is desired to provide a film and process which eliminates the need for liquid adhesives to adhere weatherable films such as monolayer AES-type films to a desired substrate.
Other coextruded film structures are also known. For example, U.S. Pat. Nos. 4,680,234 and 4,724,186 disclose weatherable coextruded flexible films and laminated structures thereof. The weatherable film layer comprises a blend of a vinyl chloride polymer, an interpolymer comprising ethylene and at least one carboxylic acid or ester thereof containing ethylenic unsaturation, and a chlorinated polyolefin. The other co-extrudates of the multilayer coextruded film of U.S. Pat. Nos. 4,680,234 and 4,724,186 can be an adhesive layer and optionally an interlayer comprising a copolymer of ethylene and vinyl acetate.
While a coextruded film structure having an adhesive layer, an interlayer and a weatherable resistant layer of a blend is disclosed in the above patents, AES and ASA-type films are not readily adherable to polyolefin polymers, metal, cellulosic materials or some other polymeric substrates. The chlorinated polyethylene (CPE) and polyvinylchloride (PVC) blends disclosed in U.S. Pat. Nos. 4,680,234 and 4,729,186 have generally low 1% secant modulus value of less than 150,000 psi. It is desired to produce a higher modulus, higher hardness and more scratch resistant polymeric surface than that which is achieved using the teachings of U.S. Pat. Nos. 4,680,234 and 4,729,186. Thus, there still exists a need in the industry for a multi-layered weatherable coextruded film which has good adhesion and is readily adherable to multiple substrates such as wood, metal, plastic and other structural substrates.
There is also a need in the industry to provide an economical coextruded film which is reprocessable i.e., a film which allows scrap material or rejects to be recycled readily.
In addition, there is still a need in the industry for a film having exceptional stability to ultraviolet light degradation and improved weathering characteristics.